The disclosed technology relates to a lubricant, suitable for use in an internal combustion engine, which containing a metal-containing detergent which provides basicity to the lubricant. A defined dispersant is present, leading to superior retention of the basicity (TBN, ASTM D 974) during use of the lubricant.
Lubrication of internal combustion engines has been a practice for many decades, yet continual improvement in lubricant technology is ongoing as new engines and new standards have been developed. Formulations directed to passenger car engines, for instance, must address limits placed on sulfated ash, phosphorus, and sulfur content (“SAPS”), and restrictions in these components often lead to upper limits on the amount of metal-containing detergent that can be included in the lubricant. One of the benefits that metal-containing detergents provide to the lubricant is basicity (measurable as TBN), which is available for various functions, including neutralization of acidic byproducts of combustion. At the same time, some engine tests specify a minimum TBN level remaining at the end of the test. Therefore, “TBN retention” has become an important parameter in design and selection of engine lubricants. Good TBN retention is associated with the ability of a lubricant to protect the engine from corrosive wear and maintaining that protection over an extended period of time.
The disclosed technology, therefore, solves the problem of providing good TBN retention (and associated benefits) by selection of a suitable dispersant, as described herein. The desirable dispersants typically have a high total acid number (TAN).